The use of spirit-levels (also sometimes known as bubble levels) and other related leveling devices (such as clinometers) in a variety of engineering and domestic settings is well known in the art. In its most usual form, the spirit-level consists of a rigid-walled, transparent vial or capsule partially filled with a liquid, into which is entrapped a bubble. By means of suitable markings placed either on the capsule itself or on a base member supporting said capsule, the user is able to determine when the device is placed in a level orientation in relation to a desired plane. This simple spirit-level design has changed little over the years and is generally recognized as having the advantages of simplicity of construction and reasonable accuracy.
One significant drawback of the basic spirit-level design, however, is the difficulty commonly encountered in reading the device. This difficulty is essentially one of insufficient contrast or visual differentiation between the liquid contained in the vial and the bubble entrapped therein. This problem is further exacerbated by the poor lighting conditions that prevail in many of the working environments in which spirit-levels are used.
Many attempts have been made over the years to overcome the problem of poor visibility or readability of spirit-levels. The attempted improvements made to the basis design include the addition of one or more of the following structural features: a reflective surface beneath the fluid-containing vial, a color-contrasting background, fluorescent liquids within the vial, externally placed viewing prisms (in order to accentuate the differences in refractive index of the liquid and the bubble) and illumination of the vial. These various prior art attempts are reviewed in U.S. Pat. Nos. 4,164,077 and 4,407,075.
It may be readily be appreciated from the foregoing partial list of prior art approaches that all of the previous attempts to increase the contrast between the liquid within the vial and the bubble suspended therein have focused either on changing the visual properties of the liquid (either directly, or by the use of contrasting backgrounds) or on increasing the overall illumination levels. While some of the abovementioned prior art approaches have led to partial improvements in readability, a need still exists for a spirit-level vial having substantially increased contrast between the liquid and the suspended bubble.
The aim of the present invention, which will shortly be disclosed and described hereinbelow, is to provide a spirit-level vial having significantly improved readability.
A further aim of the present invention is to provide an improved spirit-level vial in which the increased visual contrast between the vial liquid and the bubble suspended therein is obtained by altering the structure and properties of said bubble.
It is a still further purpose of the invention to provide a spirit-level vial that overcomes the disadvantages of prior art vials.
Further objects and advantages of the present invention will become apparent as the description proceeds.